Organic electrolytic cell

ABSTRACT

PCT No. PCT/JP94/01557 Sec. 371 Date Mar. 21, 1996 Sec. 102(e) Date Mar. 21, 1996 PCT Filed Sep. 22, 1994 PCT Pub. No. WO95/08852 PCT Pub. Date Mar. 30, 1995There is provided an organic electrolytic cell equipped with a positive electrode, a negative electrode and a solution of a lithium salt in an aprotic organic solvent as an electrolytic solution, wherein (1) the positive electrode contains a metallic oxide, (2) the negative electrode is an infusible, insoluble substrate (PAS) having a polyacene type skeletal structure and a hydrogen/carbon atomic ratio of 0.5 to 0.05, the substrate being a heat-treated product of an aromatic condensation polymer, and (3) the total amount of lithium contained in the cell is 500 mAh/g or more, and the amount of lithium originating in the negative electrode is 100 mAh/g or more, based on the infusible, insoluble substrate (PAS) having a polyacene type skeletal structure as the negative electrode, the organic electrolytic cell being a secondary cell having a high capacity and high voltage.

BACKGROUND OF THE INVENTION

The present invention relates to an organic electrolytic cell having ahigh capacity and high voltage, wherein an infusible, insolublesubstrate having a polyacene type skeletal structure is used as thenegative electrode, and a metallic oxide is used as the positiveelectrode.

In recent years, a secondary cell wherein an electrically conductivemacromolecule, an oxide of a transition metal or the like is used as thepositive electrode, and metallic lithium or a lithium alloy is used asthe negative electrode has been proposed as a cell to be used in placeof Ni-Cd storage cells and lead storage cells, because of its highenergy density.

However, when such a secondary cell is subjected to repeated charge anddischarge, its capacity is largely lowered due to deterioration of thepositive electrode or negative electrode, and thus there still remains aproblem in its practical aspect. Particularly by deterioration of thenegative electrode, mossy lithium, called dendrites, are formed, andthrough repeated charge and discharge, the dendrites finally penetratesthe separator and causes a short circuit, and in some case the cell isruptured, and thus there has been a problem in its safety, too.

Recently, for solving the above problems, there has been proposed a cellwherein a carbonic material, such as graphite, is used as the negativeelectrode, and a lithium-containing metallic oxide, such as LiCoO₂, isused as the positive electrode. The cell is a so-called rockingchair-type cell wherein after assembly of the cell, lithium is suppliedfrom the lithium-containing metallic oxide as the positive electrode tothe negative electrode through charge, and lithium of the negativeelectrode is returned to the positive electrode through discharge.Although the cell is characterized by a high voltage and high capacity,its capacity is at most on the order of 80 to 90 mAh/cc (based on thetotal volumes of the electrodes; the separator and the currentcollectors); the high energy density which is a characteristic oflithium cells has not been obtained.

On the other hand, an infusible, insoluble substrate having a polyacenetype skeletal structure and having a hydrogen/carbon atomic ratio of 0.5to 0.05, which is a heat-treated product of an aromatic condensationpolymer, can be doped with a larger amount of lithium, compared withgeneral carbonic materials. However, when a cell was assembled using theinfusible, insoluble substrate, its capacity was not adequatelysatisfactory.

SUMMARY OF THE INVENTION

Thus, the first object of the present invention lies in providing asecondary cell having a high capacity and high voltage.

Another object of the invention lies in providing such a secondary cellthat charge and discharge are possible over a long term and is excellentin safety.

Still another object of the invention lies in providing a secondary cellwhich is easy to prepare.

Still another object of the invention will be apparent from thefollowing description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial sectional view illustrating the structure of a firstembodiment of the cell of the invention and

FIG. 2 is a cutout view illustrating the structure of a secondembodiment of the cell of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present inventors found that for attaining the above objects andadvantages, it is important to use a metallic oxide as the positiveelectrode and an infusible, insoluble substrate having a polyacene typeskeletal structure as the negative electrode, and control the amount oflithium in the cell appropriately.

More detailedly, it was found that the above objects and advantages canbe accomplished by an organic electrolytic cell equipped with a positiveelectrode, a negative electrode and a solution of a lithium salt in anaprotic organic solvent as an electrolytic solution, wherein

(1) the positive electrode is one containing a metallic oxide,

(2) the negative electrode is an infusible, insoluble substrate having apolyacene type skeletal structure and a hydrogen/carbon atomic ratio of0.5 to 0.05, said substrate being a heat-treated product of an aromaticcondensation polymer (hereinafter referred to as PAS), and

(3) the total amount of lithium contained in the cell is 500 mAh/g ormore, and the amount of lithium originating in the negative electrode is100 mAh/g or more, based on the negative electrode PAS.

The aromatic condensation polymer in the invention is a condensate of anaromatic hydrocarbon compound with an aldehyde. As the aromatichydrocarbon compound, so-called phenols such as, for example, phenol,cresol and xylenol are preferred. It can, for example, be amethylene-bisphenol represented by the following formula (A) ##STR1##wherein x and y are independently 0, 1 or 2, or it can also be ahydroxy-biphenyl or a hydroxy-naphthalene. Among them, phenols,particularly phenol are preferred in a practical aspect.

As the aromatic condensation polymer in the invention, there can also beused a modified aromatic condensation polymer wherein part of thearomatic hydrocarbon compound having phenolic hydroxyl group(s) wasreplaced with an aromatic hydrocarbon compound having no phenolichydroxyl group such as, for example, xylene, toluene or aniline, forexample, a condensate of phenol, xylene and formaldehyde, and further,there can also be used a modified aromatic polymer wherein the abovepart is replaced with melamine or urea. Further, furan resins are alsopreferred.

Further, as the aldehyde, it is possible to use aldehydes such asformaldehyde, acetaldehyde and furfural, but formaldehyde is preferred.A phenolformaldehyde condensate can be any of a novolak type, a resoltype and a mixture thereof.

The infusible, insoluble substrate in the invention can be obtained byheat treating the above aromatic polymer, and there can be used all ofthe infusible, insoluble substrates having a polyacene type skeletalstructure described in Japanese Patent Publication No. 44212/1989 (U.S.Pat. No. 4,601,849, EP 67444), Japanese Patent Publication No.24024/1991 (U.S. Pat. No. 4,615,960, EP 149497), etc., and such aninfusible, insoluble substrate can also be prepared as follows.

An infusible, insoluble substrate having a hydrogen/carbon atomic ratio(hereinafter referred to as H/C) of 0.50 to 0.05, preferably 0.35 to0.10 can be obtained by gradually heating the aromatic condensationpolymer up to a proper temperature of 400° C. to 800° C. in anon-oxidizing atmosphere (including a vacuum) such as nitrogen or argon.

It is also possible to obtain an infusible, insoluble substrate having aspecific surface area, measured by the BET method, of 600 m² /g or moreaccording to the method described in Japanese Patent Publication No.24024/1991 (U.S. Pat. No. 4,615,960, EP 149497), or the like. Forexample, an infusible, insoluble substrate having the above H/C andhaving a specific surface area, measured by the BET method, of, e.g.,600 m² /g or more can also be obtained, for example, by preparing asolution containing an initial condensate of an aromatic condensationpolymer and an inorganic salt such as zinc chloride; heating thesolution to cure it in a mold; gradually heating the cured matter, in anon-oxidizing atmosphere (including a vacuum), up to a temperature of350° C. to 800° C., preferably up to a proper temperature of 400° C. to750° C.; and then sufficiently washing it with water, dilutedhydrochloric acid or the like.

As to an infusible, insoluble substrate used in the invention, accordingto X-ray diffraction (CuKα), the main peak is observed at 2θ=24° orless, and besides the main peak, another peak is observed between 2θ=41°and 2θ=46°.

Namely, it is suggested that the infusible, insoluble substrate has apolyacene type skeletal structure wherein an aromatic polycyclicstructure was moderately developed, and takes an amorphous structure,and thus the substrate can be doped stably with lithium, and therefore,is useful as an active material for cells.

When H/C is above 0.50, the aromatic polycyclic structure does notsufficiently develop, and thus it is impossible to conduct doping andundoping of lithium smoothly, and when a cell is assembled, charge anddischarge efficiency is lowered. On the other hand, when H/C is lessthan 0.05, the capacity of the cell of the invention is lowered, whichis undesirable.

The negative electrode of the invention is composed of the infusible,insoluble substrate (hereinafter referred to as PAS), and practically,it is desirable to use a form obtained by forming PAS in an easilyformable form such as a powdery form, a granular form or a short fiberform with a binder.

As the binder, a fluorine binder is preferred, and a fluorine binderhaving a fluorine/carbon atomic ratio (hereinafter referred to as F/C)of under 1.5 but 0.75 or more is further preferred, and afluorine-containing polymer binder having a F/C atomic ratio of under1.3 but 0.75 or more is particularly preferred.

As the fluorine binder, there can, for example, be mentionedpolyvinylidene fluoride, a vinylidene fluoride-ethylene trifluoridecopolymer, an ethylene-ethylene tetrafluoride copolymer, apropylene-ethylene tetrafluoride copolymer, etc., and further, it isalso possible to use a fluorine-containing polymer wherein hydrogens atthe principal chain are replaced with alkyl groups. In the case ofpoly-vinylidene fluoride, F/C is 1, and in the case of the vinylidenefluoride-ethylene trifluoride copolymer, when the molar fractions ofvinylidene fluoride are 50% and 80%, F/C values become 1.25 and 1.1,respectively, and in the case of the propylene-ethylene tetrafluoridecopolymer, when the molar fraction of propylene is 50%, F/C becomes0.75. Among them, polyvinylidene fluoride, and a vinylidenefluoride-ethylene trifluoride copolymer wherein the molar fraction ofvinylidene fluoride is 50% or more are preferred, and practically,polyvinylidene fluoride is preferred.

When these binders are used, it is possible to adequately utilize thedoping ability (capacity) with lithium which PAS has.

As the positive electrode of the organic electrolytic cell of theinvention, there can, for example, be used lithium-containing metallicoxides capable of electrochemical doping with lithium andelectrochemical undoping of lithium, which can be represented by thegeneral formula LixMyOz (M is a metal capable of taking plural valences,and can be two or more metals) such as LixCoO₂, LixNiO₂, LixMnO₂ orLixFeO₂, or oxides of transition metals such as cobalt, manganese andnickel. Particularly, a lithium-containing oxide having a voltage of 4Vor more vs Li/Li⁺ is preferred. Among them, lithium-containing cobaltoxides and lithium-containing nickel oxides are preferred.

The positive electrode in the invention is one made by forming themetallic oxide, if necessary, in addition with an electricallyconductive material and a binder, and the kinds, compositions, etc. ofthe electrically conductive material and binder can suitably bespecified.

As to the kind of the electrically conductive material, it can be apowder of a metal, such as metallic nickel, but particularly preferredare carbonic materials such as, for example, active carbon, carbonblack, acetylene black and graphite. Its mixing ratio is varieddepending on the electric conductivity of the active substance, theshape of the electrode, etc., but it is suitable to add it in an amountof 2 to 40% based on the active substance.

Further, as to the kind of the binder, any binder can be used so long asit is insoluble in the later-described electrolytic solution which isused in the invention, and there can, for example, preferably be usedrubber binders such as SBR, fluorine-containing resins such aspolyethylene tetrafluoride and polyvinylidene fluoride, andthermoplastic resins such as polypropylene and polyethylene, and itsmixing ratio is preferably 20% or less.

The positive electrode and negative electrode used in the invention cantake various shapes, for example, plate-like, film-like and cylindricalshapes, and a such that the electrode is formed on metallic foil.Particularly, an electrode obtained by forming the positive electrode orthe negative electrode on metallic foil so as to be film-like ofplate-like is preferred because such an electrode can be applied tovarious cells as an electrode which is formed on a current collector.

In the cell of the invention, it is possible to increase its capacitygreatly, compared with usual cells, by using the PAS as the negativeelectrode and appropriately controlling the amount of lithium containedin the cell.

In the invention, the total amount of lithium contained in the cell isthe total of the lithium originating in the positive electrode, lithiumoriginating in the electrolytic solution, and lithium originating in thenegative electrode.

Lithium originating in the positive electrode is lithium contained inthe positive electrode at the time of assembly of the cell, and part orall of the lithium is supplied to the negative electrode by an operation(charge or the like) of sending a current from an outer circuit. Lithiumoriginating in the electrolytic solution is lithium in the electrolyticsolution contained in the separator, the positive electrode, thenegative electrode, etc. Further, lithium originating in the negativeelectrode is lithium carried on the negative electrode PAS of theinvention (lithium other than lithium originating in the positiveelectrode and lithium originating in the electrolytic solution).

A method for carrying lithium on the negative electrode PAS is notparticularly limited, and there can, for example, be mentioned a methodwhich comprises previously doping, before assembly of a cell, thenegative electrode PAS with lithium in an electrochemical cell whereinmetallic lithium is used as a counter electrode, and then assembling athe cell; a method which comprises making electric current conductbetween the negative electrode PAS and metallic lithium in a cell by amethod, e.g. of laminating metallic lithium on the negative electrodePAS, and then doping PAS with lithium in the cell; etc.

The total amount of lithium in the cell in the invention is 500 mAh/g ormore, preferably 600 mAh/g or more based on the negative electrode PAS,and in the case of under 500 mAh/g, adequate capacity cannot beobtained.

Further, the amount of lithium originating in the negative electrode is100 mAh/g or more, preferably 150 mAh/g or more based on the negativeelectrode PAS, and in the case of under 100 mAh/g, adequate capacitycannot be obtained, even if the total amount of lithium is 500 mAh/g ormore based on the negative electrode PAS.

Although as to the amount of lithium originating in the positiveelectrode and the amount of lithium originating in the electrolyticsolution, it is sufficient if the above conditions are satisfied, it ispreferred that the amount of lithium originating in the positiveelectrode is 300 mAh/g or more based on the negative electrode PAS,namely that the amount of lithium originating in the positive electrodeis 300 mAh or more per g of the negative electrode PAS.

Further, when a lithium-containing oxide is used as the positiveelectrode, it is advantageous to make the amount of lithium originatingin the negative electrode 600 mAh/g or less based on the negativeelectrode PAS.

As the solvent constituting the electrolytic solution of the invention,an aprotic organic solvent is used. As the aprotic organic solvent,there can, for example, be mentioned ethylene carbonate, propylenecarbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone,acetonitrile, dimethoxyethane, tetrahydrofuran, dioxolane, methylenechloride, sulfolane, etc, and a mixed solvent of two or more of theseaprotic organic solvents can also be used.

Further, as an electrolyte to be dissolved in the mixed or singlesolvent, any of electrolyte capable of forming lithium ions can be used.As the electrolyte, there can, for example, be mentioned LiI, LiClO₄,LiAsF₆, LiBF₄, LiPF₆, LiHF₂, etc.

The electrolyte and the solvent are mixed in a state of sufficientdehydration to give an electrolytic solution, and for making theinternal resistance by the electrolytic solution small, it is preferredto make the concentration of the electrolyte in the electrolyticsolution at least 0.1 mole/liter or more, and usually, it is furtherpreferred to make it 0.2 to 1.5 moles/liter.

As the current collector for taking out current outside the cell, therecan, for example, be used carbon, platinum, nickel, stainless steel,aluminum, copper, etc., and when a foil-like or net-like currentcollector is used, an electrode can be given as an electrode which isformed on a current collector.

An example of the embodiments of the invention is described belowaccording to a drawing. FIG. 1 is a drawing for describing the basalconstitution of the cell according to the invention. In FIG. 1, (1) is apositive electrode, and (2) is a negative electrode. (3) and (3') arecurrent collectors connected to the respective electrodes and respectiveoutside terminals (7) and (7') so that a voltage drop does not arise.(4) is an electrolytic solution, and therein a compound capable offorming ions with which the electrodes can be doped, is dissolved in anaprotic organic solvent. The electrolytic solution is usually liquid,but for preventing leakage of the solution, it an also be used afterbeing made into gel or a solid. (5) is a separator disposed forpreventing contact between both positive and negative electrodes andholding the electrolytic solution.

The separator is made of a porous material which is durable against theelectrolytic solution, the electrode active substance, etc., has openpores and is electrically non-conductive. It can usually be a cloth, anon-woven cloth, a porous material, or the like, and composed of glassfiber, polyethylene, polypropylene or the like. To decrease the internalresistance of the cell, the separator is preferably as thin as possible.Its thickness, however, is determined by considering the amount of theelectrolytic solution held, its permeability, its strength, etc. Thepositive and negative electrodes and the separator are fixed in positionwithin a cell casing (6) in a manner not to give rise to any problem inuse. The shape, size, etc. of the electrodes can properly be determinedaccording to the shape and performance of the desired cell.

The shape of the cell of the invention can be coin-type,cylindrical-type, rectangular-type, box-type, etc., but is notparticularly limited.

As described above, as to the characteristics and advantages of theorganic electrolytic cell of the invention, the organic electrolyticcell is such a cell that PAS is used as the negative electrode, ametallic oxide is used as the positive electrode, both the amount oflithium in the cell and the amount of lithium originating in thenegative electrode PAS are appropriately controlled, and has a highcapacity and high voltage.

As described above, the basal characteristic of the organic electrolyticcell of the invention is to control the total amount of lithiumcontained in the cell to 500 mAh/g or more, and control the amount oflithium originating in the negative electrode to 100 mAh/g or more, but,further, preferred embodiments of the invention are described below.

(1) In the cell of the invention, its capacity can be greatly increased,compared with usual cells, by appropriately controlling the amount oflithium contained in the cell, as described above, and, at the sametime, controlling the pore structure of PAS used as the negativeelectrode so as to be described below.

The amount of nitrogen gas adsorbed on PAS in the invention can bemeasured as follows. Namely, 0.035 g of PAS fine particles having anaverage particle size of 15 μm obtained by grinding using a disc mill isput in the sample cell of a volumetric apparatus (made by Yuasa Ionics,Ltd. AutoSorb-1), and nitrogen gas is adsorbed at a liquid nitrogentemperature of 77° K. From the adsorption isotherm obtained, the amount(cc/g) of the gas adsorbed is plotted against the thickness t (Å) of thelayer of the gas adsorbed. t (Å) is calculated by the following equation(1). ##EQU1## wherein P/P₀ is the relative pressure of nitrogen.

In the invention, it is preferred to control the pore structure of PASused as the negative electrode so that the amount of the gas adsorbed atthe thickness of adsorbed nitrogen of 10 Å found from the above nitrogenadsorption isotherm can be 100 cc/g or less, particularly 80 cc/g orless.

In the invention, when the amount of the gas adsorbed on PAS at thethickness of adsorbed nitrogen of 10 Å is above an adequate capacitycannot be obtained. Further, in the invention, the total amount oflithium in the cell is 500 mAh/g or more, preferably 600 mAh/g or more,based on the negative electrode PAS, and in the case of under 500 mAh/g,an adequate capacity cannot be obtained.

Further, the amount of lithium originating in the negative electrode inthe invention is 100 mAh/g or more, preferably 150 mAh/g or more, basedon the negative electrode PAS, and in the case of under 100 mAh/g, anadequate capacity cannot be obtained, even if the total lithium amountis 500 mAh/g or more, based on the negative electrode PAS.

Although as to the amount of lithium originating in the positiveelectrode and the amount of lithium originating in the electrolyticsolution, it is sufficient if the above conditions are satisfied, it ispreferred that the amount of lithium originating in the positiveelectrode is 300 mAh/g or more based on the negative electrode PAS.

(2) The second preferred embodiment of the invention is described below.

As already stated, in the invention, it is preferred to use as thenegative electrode a form obtained by forming fine particles (e.g.,granular, powdery, short fiber, etc.) of an infusible, insolublesubstrate (hereinafter referred to as PAS) having a polyacene typeskeletal structure and having a hydrogen/carbon atomic ratio of 0.5 to0.05, said substrate being a heat-treated product of an aromaticcondensation polymer, using a binder, preferably a fluorine binder.

Thus, in the invention, it is advantageous that a form of fine particlesof the infusible, insoluble substrate (PAS), obtained by forming PASfine particles in an easy to make form such as a powdery form or agranular form with a binder, is used as the negative electrode, andfurther that the fine particles PAS has an average particle size of 20μm or less, and when the 50% size is 2a μm, the amount of particleshaving a particle size of 1a μm or less is 10% or more by volume ratio,and the amount of particles having a particle size of 4a μm or more is10% or more by volume ratio, and further, preferably, when the 50% sizeis 2a μm, the amount of particles having a particle size of 1a μm orless is 20% or more by volume ratio, and the amount of particles havinga particle size of 4a μm or more is 10% or more by volume ratio, andparticularly preferably, when the 50% size is 2a μm, the amount ofparticles having a particle size of 1a μm or less is 20% or more byvolume ratio, and the amount of particles having a particle size of 4aμm or more is 20% or more by volume ratio. In the invention, it isadvantageous, for obtaining a cell having a high capacity, that the fineparticles have a wide particle size distribution and an average particlesize of not more than 20 μm. When the average particle size is above 20μm, or even when the average particle size is 20 μm or less, when the50% size is 2a μm, the amount of particles having a particle size of 1aμm or less is under 10% by volume ratio, or the amount of particleshaving a particle size of 4a μm or more is under 10% by volume ratio,the capacity of the resultant cell is low, which is undesirable.

In this connection, the average particle size is a volume averageparticle size, and the 50% size is a particle size corresponding to 50%of an integration curve of particle volume (see the followingliterature). "Funtai Riron to Oyo" (Fine Particle Theory and ItsApplication), edited by Kiichiro Kubo and others, pages 450 to 453,published by Maruzen Co., Ltd. on May 12, 1969.

PAS as fine particles can be obtained by grinding an infusible,insoluble substrate obtained by heat treating a form of an aromaticpolymer. The method of grinding is not particularly limited, but it isefficient to use a grinder having both grinding mechanisms of impact andfriction, for example, a ball mill such as a pot mill or a vibratingmill. Further, in some case, PAS as fine particles can also be obtainedby classifying the powder obtained, or by mixing two or more PAS powdershaving different particle size distributions.

As the binder used in the negative electrode of the invention, afluorine binder is preferred, as stated already, and further preferredis a fluorine binder having a fluorine/carbon atomic ratio (hereinafterreferred to as F/C) of under 1.5 but 0.75 or more, and particularlypreferred is a fluorine binder having a F/C of under 1.3 but 0.75 ormore.

As the fluorine binder, there can, for example, be mentionedpolyvinylidene fluoride, a vinylidene fluoride-ethylene trifluoridecopolymer, an ethylene-ethylene tetrafluoride copolymer, apropylene-ethylene tetrafluoride copolymer, etc., and further, it isalso possible to use a fluorine-containing polymer wherein hydrogens atthe principal chain are replaced with alkyl groups.

The negative electrode of the invention is obtained by forming fineparticles of PAS with a binder, as stated already, and the porosity ofthe negative electrode is determined by impregnating the negativeelectrode with propylene carbonate at 25° C., and is preferably 40% orless. When the porosity is above 40%, even if the particle size of PASis controlled as described above, as to cells obtained therefrom,adequate capacity is hard to get.

It is preferred, as stated above, that the porosity of the negativeelectrode used in the invention is 40% or less, and according toexperience of the present inventors, cells of high capacity can beobtained, unexpectedly, even when the porosity of the negative electrodeis on the order of 25%. In the light of this fact, it is believed thatthere is no problem even if the porosity of the negative electrode is onthe order of 20%.

(3) The third preferred embodiment of the invention is described below.

As the negative electrode of the organic electrolytic cell of theinvention is preferred

a negative electrode obtained by forming an infusible, insolublesubstrate (PAS) having a polyacene type skeletal structure and ahydrogen/carbon atomic ratio of 0.5 to 0.05, said substrate being aheat-treated product of an aromatic condensation polymer, on metallicfoil using a thermoplastic binder, and then heating the resultant format a temperature equal to or higher than the melting point of thethermoplastic binder.

As stated already, as the thermoplastic binder, preferred arefluorine-containing polymer binders, particularly, a fluorine-containingpolymer having a fluorine/carbon atomic ratio of under 1.5 but 0.75 ormore, particularly polyvinylidene fluoride.

When such a binder is used, it is possible to sufficiently utilize theability (capacity) of PAS to be doped with lithium.

When, as to the negative electrode of the invention, the PAS is formedwith a binder and the resultant form is heat treated at a temperatureequal to or higher than the melting point of the thermoplastic binder,the method of heat treatment is not particularly limited, but it ispreferred to conduct the heat treatment in a non-oxidizing atmosphere inthe range of from a temperature higher by 5° C. than the melting pointto a temperature higher by 100° C. than the melting point. When the heattreatment is not conducted, for example when the negative electrode PASformed on the metallic foil is doped with lithium in an electrochemicalcell wherein metallic lithium is used as a counter electrode, and then acell is assembled using the doped negative electrode PAS, there arises aphenomena, e.g. that the flexural strength of the electrode is weakened,peeling of the electrode is liable to occur, and further, the internalresistance of the assembled cell increases, and as a result, it becomesdifficult to get sufficient capacity.

When, in the invention, an infusible, insoluble substrate (PAS) having apolyacene type skeletal structure is formed on a metallic foil using athermoplastic binder, preferably a fluorine-containing polymer binder,the forming is conducted, for example by sufficiently mixing theinfusible, insoluble substrate, the fluorine-containing polymer, and asolvent or dispersion medium, and then forming the mixture. The amountof the fluorine-containing polymer varies depending on the shape andparticle size of the infusible, insoluble substrate, the strength andshape of the desired electrode, etc., but is preferably 2% to 50%, morepreferably 5% to 30% by weight based on the infusible, insolublesubstrate. As the solvent, preferred are solvents capable of dissolvingthe fluorine-containing polymer such as N,N-dimethylformamide,N-methylpyrrolidone and N,N-dimethylacetamide. In the above mixture, itdoes not become a particular problem whether the fluorine-containingpolymer is completely dissolved, or only part thereof is dissolved, butit is preferred for obtaining a homogeneous electrode that thefluorine-containing polymer is completely dissolved. Further, theviscosity of the mixture can be controlled by the amount of the solvent,and for example, it is possible to form the mixture adjusted to a highviscosity into a sheet using a roller or the like, and it is alsopossible to obtain an extremely thin electrode having a thickness, e.g.of 100 μm or less by applying a mixed slurry adjusted to a low viscosityonto metallic foil, drying it and if necessary, pressing it.Particularly, when an excellent flexibility is desired, an applicationforming method is desirable.

The positive electrode and negative electrode used in the invention cantake various shapes, for example, plate-like, film-like and cylindricalshapes, and a shape such that the electrode is formed on metallic foil.Particularly, an electrode obtained by forming the positive electrode orthe negative electrode on metallic foil is preferred because such anelectrode can be applied to various cells as an electrode which isformed on a current collector.

(4) The fourth preferred embodiment of the invention is described below.

Further, in the organic electrolytic cell of the invention, it ispreferred wherein

i) the negative electrode is an infusible, insoluble substrate (PAS)having a polyacene type skeletal structure and a hydrogen/carbon atomicratio of 0.5 to 0.05, said substrate being a heat-treated product of anaromatic condensation polymer,

ii) the total amount of lithium contained in the cell is 500 mAh/g ormore, and the amount of lithium originating in the negative electrode is100 mAh/g or more, based on the negative electrode PAS, and

iii) lithium originating in the negative electrode is previously carriedon PAS before assembly of the cell.

Lithium originating in the negative electrode in the invention islithium carried on the negative electrode PAS of the invention (lithiumother than lithium originating in the positive electrode and lithiumoriginating in the electrolytic solution).

In the above preferred embodiment of the invention, a method forcarrying lithium on the negative electrode PAS is not particularlylimited so long as it is possible by the method to carry lithium on thenegative electrode PAS before assembly of the cell. For example, it ispossible to previously carry lithium on the negative electrode PAS bypassing a constant current or applying a constant voltage in anelectrochemical cell wherein metallic lithium is used as a counterelectrode. When lithium is carried on the negative electrode PAS afterassembly of the cell, for example, when a method is taken whichcomprises making current conduct between the negative electrode PAS andmetallic lithium in a cell by a method, e.g. of laminating metalliclithium on the negative electrode PAS, and then doping PAS with lithiumin the cell, not only is the capacity as a practical cell lowered, but,e.g., the internal resistance of the cell increases, which isundesirable.

Even in this case, it is advantageous that the total amount of lithiumcontained in the cell is 500 mAh/g or more, preferably 600 mAh/g ormore, based on the negative electrode PAS, and in the case of under 500mAh/g, sufficient capacity cannot be obtained.

Further, the amount of lithium originating in the negative electrode inthe invention is 100 mAh/g or more, preferably 150 mAh/g or more, basedon the negative electrode PAS, and in the case of under 100 mAh/g,adequate capacity cannot be obtained, even if the total lithium amountis 500 mAh/g or more based on the negative electrode PAS. Further, whena lithium-containing oxide is used in the positive electrode, it ispractical to make the amount of lithium originating in the negativeelectrode 600 mAh/g or less based on the negative electrode PAS, asstated already.

Although as to the amount of lithium originating in the positiveelectrode and the amount of lithium originating in the electrolyticsolution, it is sufficient if the above conditions are satisfied, and itis preferred that the amount of lithium originating in the positiveelectrode is 300 mAh/g or more based on the negative electrode PAS.

An example of still other embodiments of the invention is describedbelow according to a drawing. FIG. 2 is a drawing for describing thebasal constitution of the cell according to the invention. In FIG. 2,(1) is a positive electrode, and (2) is a negative electrode. (3) and(3') are current collectors, and each electrode is formed on eachcurrent collector. Lead terminals (10) and (10') are connected to therespective current collectors so that a voltage drop does not arise, andthe other ends are connected to a cell casing (6) and a top cap (9). (5)is a separator impregnated with an electrolytic solution, and in theelectrolytic solution, the aforesaid compound capable of forming ionswith which doping is made is dissolved in an aprotic organic solvent.The electrolytic solution is usually a liquid, and impregnated into theseparator, but it can also be used, without any separator, after beingmade into gel or a solid for preventing leakage of the solution. (8) isan insulating packing for preventing contact between both positive andnegative electrodes (the cell casing and the top cap).

The separator is made of a porous material which is durable against theelectrolytic solution, the electrode active substance, etc., has openpores and is electrically non-conductive. It can usually be a cloth, anon-woven cloth, a porous material, or the like and is composed of glassfiber, polyethylene, polypropylene or the like. To decrease the internalresistance of the cell, the separator is preferably as thin as possible.Its thickness, however, is determined by considering the amount of theelectrolytic solution held, its permeability, its strength, etc. Thepositive and negative electrodes and the separator are fixed in positionwithin the cell casing (6) in a manner not to give rise to any problemsin use. The shape, size, etc. of the electrodes can properly bedetermined according to the shape and performance of the desired cell.

The shape of the cell of the invention is not limited to the cylindricalshape as exemplified above, but can also be coin-type, rectangular-type,box-type, etc., and is not particularly limited.

(5) The fifth preferred embodiment of the invention is described below.

In the invention, in the case of preparing an organic electrolytic cellequipped, as stated already, with a positive electrode, a negativeelectrode and a solution of a lithium salt in an aprotic organic solventas an electrolytic solution, wherein

(1) the positive electrode contains a metallic oxide,

(2) the negative electrode is an infusible, insoluble substrate (PAS)having a polyacene type skeletal structure and having a hydrogen/carbonatomic ratio of 0.5 to 0.05, said substrate being a heat-treated productof an aromatic condensation polymer, and

(3) the total amount of lithium contained in the cell is 500 mAh/g ormore, and the amount of lithium originating in the negative electrode is100 mAh/g or more, based on the negative electrode PAS,

it is preferred to electrochemically carry lithium originating in thenegative electrode on the negative electrode by applying an electricpotential equal to or less than the electric potential of metallic Li tothe negative electrode.

In the invention, as stated already, the total amount of lithiumcontained in the cell is the total of lithium originating in thepositive electrode, lithium originating in the electrolytic solution,and lithium originating in the negative electrode.

Lithium originating in the positive electrode is lithium contained inthe positive electrode at the time of assembly of the cell, and part orall of the lithium is supplied to the negative electrode by an operation(charge or the like) of sending a current from an outer circuit. Lithiumoriginating in the electrolytic solution is lithium in the electrolyticsolution contained in the separator, the positive electrode, thenegative electrode, etc. Further, lithium originating in the negativeelectrode is lithium carried on the negative electrode PAS of theinvention (lithium other than lithium originating in the positiveelectrode and lithium originating in the electrolytic solution).

In the invention, as to a method of carrying lithium on the negativeelectrode PAS, it is possible to previously carry lithium on thenegative electrode PAS by, before assembly of the cell, passing aconstant current or applying a constant voltage or using a combinationthereof, in an electrochemical cell wherein metallic lithium is used asa counter electrode.

In the invention, in previously carrying lithium on the negativeelectrode PAS, it is particularly preferred to apply an electricpotential equal to or less than the electric potential of metalliclithium, at least once, to the negative electrode PAS, based on theelectric potential of metallic lithium. The voltage to be applied isvaried depending on the desired amount of lithium originating in thenegative electrode, PAS, the kind and shape of the electrodes, and thekind and shape of the electrolytic cell, but is preferably 0 mV to-1,000 mV, more preferably -10 mV to -300 mV based on the electricpotential of metallic lithium. An important thing is to select such avoltage to be as low as possible so that metallic lithium does notelectrodeposit, and in some cases, it is possible to first carry lithiumat an electric potential equal to or less than the electric potential ofmetallic lithium, gradually increase the voltage, and finally completethe carrying at a positive electric potential, or it is also possible toconduct the carrying first at a positive electric potential and then atan electric potential equal to or less than the electric potential ofmetallic lithium.

The total amount of lithium contained in the cell is 500 mAh/g or more,preferably 600 mAh/g or more, based on the negative electrode PAS, andin the case of under 500 mAh/g, a sufficient capacity cannot beobtained.

Further, the amount of lithium originating in the negative electrode inthe invention is 100 mAh/g or more, preferably 150 mAh/g or more, basedon the negative electrode PAS, and in the case of under 100 mAh/g, anadequate capacity cannot be obtained, even if the total lithium amountis 500 mAh/g or more based on the negative electrode PAS. Further, whena lithium-containing oxide is used in the positive electrode, it ispractical to make the amount of lithium originating in the negativeelectrode 600 mAh/g or less, based on the negative electrode PAS.

Although as to the amount of lithium originating in the positiveelectrode and the amount of lithium originating in the electrolyticsolution, it is sufficient if the above conditions are satisfied and, itis preferred that the amount of lithium originating in the positiveelectrode is 300 mAh/g or more, based on the negative electrode PAS.

(6) Further, the sixth preferred embodiment of the invention isdescribed below.

In the invention, in previously carrying, as stated in the above (4),lithium originating in the negative electrode on PAS before assembly ofthe cell, it is particularly preferred to electrochemically carrylithium originating in the negative electrode using a solution of alithium salt in a cyclic carbonate solvent.

In this connection, the lithium salt is an electrolyte capable offorming lithium ions such as, for example, LiClO₄, LiAsF₆, LiBF₄ andLiPF₆, and as the cyclic carbonate solvent, there can be used a singlesolvent such as ethylene carbonate or propylene carbonate, or a mixedsolvent of two or more thereof. The above electrolyte and solvent aremixed in a state of sufficient dehydration to give an electrolyticsolution and for making the internal resistance due to the electrolyticsolution small, it is preferred to make the concentration of theelectrolyte in the electrolytic solution at least 0.1 mole/liter, andusually, it is further preferred to make the concentration 0.2 to 1.5moles/liter. A method for previously carrying lithium on the negativeelectrode PAS is not particularly limited so long as it is possible toaccomplish the purpose, and for example, it is possible to previouslycarry lithium on the negative electrode PAS by using the electrolyticsolution, and passing a constant current or applying a constant voltagein an electrochemical cell wherein metallic lithium is used as a counterelectrode.

According to the invention described above, there is provided an organicelectrolytic cell which is easy to prepare, and is usable as a secondarycell having a high capacity and high voltage.

Further, the organic electrolytic cell of the invention can be such asecondary cell that charge and discharge is possible over a long periodand it is excellent in safety.

A secondary cell having a particularly high capacity is provided bycombining one or more of the above-mentioned first, second, third,fourth, fifth and sixth preferred embodiments of the invention.

Further, the third and fourth preferred embodiments of the invention areadvantageous because thereby are provided secondary cells having lowinternal resistance and high capacity.

Further, the above fifth preferred embodiment of the invention has anadvantage of making it possible to prepare the above secondary cellhaving a high capacity and high voltage more easily.

The invention is described below by examples. However, the followingexamples are for specifically describing the embodiments of theinvention, and the invention is not limited to the following examples atall, and is not restricted thereby at all.

The basal constitution of the cell according to the invention shown inthe attached drawing FIG. 1 is as follows.

1 Positive electrode

2 Negative electrode

3, 3' Current collector

4 Electrolytic solution

5 Separator

6 Cell casing

7, 7' Outside terminals

Further, the basal constitution of the cell according to the inventionshown in the attached drawing FIG. 2 is as follows.

1 Positive electrode

2 Negative electrode

3 Current collector (positive electrode)

3' Current collector (negative electrode)

8 Insulating packing

5 Separator

6 Cell casing

9 Top cap

10 Terminal (positive electrode)

10' Terminal (negative electrode)

EXAMPLE 1

A phenol-formaldehyde resin forming plate 0.5 mm thick was put in asilicon carbide heating element, the inside temperature was increased ata rate of 10° C./hour in an atmosphere of nitrogen, and heat treatmentwas conducted up to 650° C. to synthesize an infusible, insolublesubstrate (referred to as PAS). The resultant PAS plate was ground usinga disc mill to give PAS powder having an average particle size of 15 μm.Its H/C ratio was 0.22.

Then, 100 weight parts of the PAS powder, and 100 weight parts of asolution of 10 weight parts of polyvinylidene fluoride powder in 90weight parts of N,N-dimethylformamide were adequately mixed to give aslurry. The slurry was applied onto a copper foil 10 μm thick (a currentcollector for the negative electrode) using an applicator, heat-dried,and pressed to give a PAS negative electrode 110 μm thick.

50 weight parts of a solution of 10 weight parts of polyvinylidenefluoride powder in 90 weight parts of N,N-dimethylformamide wasadequately mixed with 100 parts of commercially available LiCoO₂ (madeby Strem Chemicals Co.) and 5 parts of graphite to give a slurry. Theslurry was applied an aluminum foil 20 μm thick (a current collector forthe positive electrode) using an applicator, dried, and pressed to givea PAS positive electrode 1 having a thickness of 150 μm.

The above negative electrode was doped with lithium in amounts of 150mAh/g, 200 mAh/g and 300 mAh/g, based on the negative electrode PAS, ata constant current (a current was sent whereby 30 mAh/g of lithium couldbe carried per hour on the negative electrode PAS), using lithium as acounter electrode and using a solution of LiPF₆ at a concentration of 1mole/liter in a 1:1 (weight ratio) mixed solvent of propylene carbonateand diethyl carbonate as an electrolytic solution, whereby the lithiumwas carried thereon (lithium originating in the negative electrode). Theresultant negative electrodes were designated Negative electrodes 1, 2and 3, respectively.

Three kinds of cells as shown in FIG. 1 were assembled using the abovepositive electrode and Negative electrodes 1, 2 and 3 (each 1×1 cm²). Asthe separator, a polypropylene separator 25 μm thick was used. Further,as the electrolytic solution a solution of LiPF₆ was used at aconcentration of 1 mole/liter in a 1:1 (weight ratio) mixed solvent ofpropylene carbonate and diethyl carbonate. The total lithium amount inthe cell based on the negative electrode PAS is shown in Table 1.

Each of the above cells was charged at a constant current of 0.25 mA/cm²until the cell voltage became 4.3 V, and successively, discharged at aconstant current of 0.25 mA/cm² until the cell voltage became 2.5 V.This 4.3 V-2.5 V cycle was repeated, and in the third discharge, anevaluation was made using volume capacity (mAh/cc). As the volumestandard, the total of the electrode volumes, the separator volume andthe current collector volumes was used. The results are shown in thefollowing Table 1.

                  TABLE 1                                                         ______________________________________                                                         Total lithium                                                                            Lithium amount                                                     amount in the                                                                            originating in the                                                                      Volume                                  Positive                                                                              Negative cell       negative electrode                                                                      capacity                                electrode                                                                             electrode                                                                              (mAh/g)    (mAh/g)   (mAh/cc)                                ______________________________________                                        1       1        890        150       131                                     1       2        940        200       141                                     1       3        1040       300       155                                     ______________________________________                                    

EXAMPLE 2

Positive electrodes having thicknesses of 100 μm and 200 μm wereobtained in the same manner as in Example 1, and designated Positiveelectrode 2 and Positive electrode 3, respectively.

Cells were assembled in the same manner as in Example 1 usingcombinations of Positive electrode 2 with Negative electrode 2, andPositive electrode 3 with Negative electrode 3, and an evaluation wasmade using volume capacity. The results are shown in the following Table2.

                  TABLE 2                                                         ______________________________________                                                         Total lithium                                                                            Lithium amount                                                     amount in the                                                                            originating in the                                                                      Volume                                  Positive                                                                              Negative cell       negative electrode                                                                      capacity                                electrode                                                                             electrode                                                                              (mAh/g)    (mAh/g)   (mAh/cc)                                ______________________________________                                        2       2         680       200       121                                     3       2        1190       200       146                                     ______________________________________                                    

Comparative Example 1

Positive electrode 4 having a thickness of 260 μm was obtained in thesame manner as in Example 1. As the negative electrode, Negativeelectrode 4 on which lithium was not previously carried was used. Cellswere assembled in the same manner as in Example 1 using combinationsbetween Positive electrodes 1, 3 or 4 and Negative electrode 4, and anevaluation was made using volume capacity. The results are shown in thefollowing Table 3.

                  TABLE 3                                                         ______________________________________                                                         Total lithium                                                                            Lithium amount                                                     amount in the                                                                            originating in the                                                                      Volume                                  Positive                                                                              Negative cell       negative electrode                                                                      capacity                                electrode                                                                             electrode                                                                              (mAh/g)    (mAh/g)   (mAh/cc)                                ______________________________________                                        1       4        740        0          95                                     3       4        990        0         104                                     4       4        1350       0         105                                     ______________________________________                                    

When the lithium amount originating in the negative electrode is 0,sufficient capacity was not obtained, however large the total lithiumamount in the cell.

Comparative Example 2

Negative electrode 5 was obtained in the same manner as in Example 1except that the lithium amount to be previously carried was changed to50 mAh/g. A cell was assembled in the same manner as in Example 1 usinga combination between Positive electrode 1 and Negative electrode 5, andan evaluation was made using volume capacity. The results are shown inthe following Table 4.

                  TABLE 4                                                         ______________________________________                                                         Total lithium                                                                            Lithium amount                                                     amount in the                                                                            originating in the                                                                      Volume                                  Positive                                                                              Negative cell       negative electrode                                                                      capacity                                electrode                                                                             electrode                                                                              (mAh/g)    (mAh/g)   (mAh/cc)                                ______________________________________                                        1       5        790        50        103                                     ______________________________________                                    

When the lithium amount originating in the negative electrode (in thisexample, lithium with which the previous doping was made) was small,sufficient capacity was not obtained, even if the total lithium amountin the cell is sufficient.

(1) Examples of the first preferred embodiment of the invention are setforth below.

EXAMPLE 3

50 weight parts of a xylene resin (made by Lignte Co.), 50 weight partsof novolak (made by Showa Kobunshi Co. Ltd.) and 0.1 weight part ofxylenesulfonic acid were heated at 100° C. to give a xylene-modifiednovolak resin. 10 weight parts of hexamethylenetetramine was mixed with100 weight parts of the resin, and the mixture was ground and thenformed by thermal pressing into a formed plate.

The formed plate of the xylene-modified novolak resin was put in asilicon carbide heating element, the inside temperature was increased ata rate of 10° C./hour in an atmosphere of nitrogen, and heat treatmentwas conducted up to 650° C. to synthesize an infusible, insolublesubstrate (referred to as PAS). The resultant PAS plate was ground usinga disc mill to give PAS powder having an average particle size of 15 μm.Its H/C ratio was 0.22. The amount of gas adsorbed on the PAS fineparticles at a nitrogen adsorption thickness of 10 Å was 29 cc/g.

Then, 100 weight parts of the PAS powder, and 100 weight parts of asolution of 10 weight parts of polyvinylidene fluoride powder in 90weight parts of N,N-dimethylformamide were adequately mixed to give aslurry. The slurry was applied onto a copper foil 10 μm thick (a currentcollector for the negative electrode) using an applicator, dried, andpressed to give a PAS negative electrode 110 μm thick.

50 weight parts of a solution of 10 weight parts of polyvinylidenefluoride powder in 90 weight parts of N,N-dimethylformamide wasadequately mixed with 100 parts of commercially available LiCoO₂ (madeby Strem Chemicals Co.) and 5 parts of graphite to give a slurry. Theslurry was applied onto an aluminum foil 20 μm thick (a currentcollector for the positive electrode) using an applicator, dried, andpressed to give a PAS positive electrode 5 having a thickness of 165 μm.

The above negative electrode was doped with lithium in amounts of 150mAh/g, 200 mAh/g and 300 mAh/g based on the negative electrode PAS at aconstant current (a current was sent whereby 30 mAh/g of lithium couldbe carried per hour on the negative electrode PAS), using lithium as acounter electrode and using a solution of LiPF₆ at a concentration of 1mole/liter in a 1:1 (weight ratio) mixed solvent of propylene carbonateand diethyl carbonate as an electrolytic solution, whereby the lithiumwas carried thereon (lithium originating in the negative electrode). Theresultant negative electrodes were designated Negative electrodes 6, 7and 8, respectively. Three kinds of cells as shown in FIG. 1 wereassembled using the above positive electrode and Negative electrodes 6,7 and 8 (each 1×1 cm²). As the separator, a polypropylene separator 25μm thick was used. Further, as the electrolytic solution, a solution ofLiPF₆ at a concentration of 1 mole/liter in a 1:1 (weight ratio) mixedsolvent of propylene carbonate and diethyl carbonate was used. The totallithium amount in the cell based on the negative electrode PAS is shownin Table 5.

Each of the above cells was charged at a constant current of 0.25 mA/cm²until the cell voltage became 4.3 V, and successively, discharged at aconstant current of 0.25 mA/cm² until the cell voltage became 2.5 V.This 4.3 V-2.5 V cycle was repeated, and in the third discharge, anevaluation was made using volume capacity (mAh/cc). As the volumestandard the total of the electrode volumes, the separator volume andthe current collector volumes was used. The results are shown in thefollowing Table 5.

                  TABLE 5                                                         ______________________________________                                               Nitrogen                                                                      adsorption                                                                    amount at an                                                                            Total lithium                                                                            Lithium amount                                           adsorption                                                                              amount in the                                                                            originating in the                                                                      Volume                                  Negative                                                                             thickness of                                                                            cell       negative electrode                                                                      capacity                                electrode                                                                            10 Å (cc/g)                                                                         (mAh/g)    (mAh/g)   (mAh/cc)                                ______________________________________                                        6      29         990       150       151                                     7      29        1020       200       157                                     8      29        1130       300       171                                     ______________________________________                                    

EXAMPLE 4

Negative electrodes were obtained in the same manner as in Example 3except that the composition of the raw materials for PAS was changed to30 weight parts of the xylene resin and 70 weight parts of the novolak,or 10 weight parts of the xylene resin and 90 weight parts of thenovolak. The resultant negative electrodes were doped respectively withlithium in amounts of 300 mAh/g based on the negative electrode PAS,whereby the lithium was carried thereon to give Negative electrode 9 andNegative electrode 10, respectively.

Cells were assembled in the same manner as in Example 3, and anevaluation was made using volume capacity. The results are shown in thefollowing Table 6.

                  TABLE 6                                                         ______________________________________                                               Nitrogen                                                                      adsorption                                                                    amount at an                                                                            Total lithium                                                                            Lithium amount                                           adsorption                                                                              amount in the                                                                            originating in the                                                                      Volume                                  Negative                                                                             thickness of                                                                            cell       negative electrode                                                                      capacity                                electrode                                                                            10 Å (cc/g)                                                                         (mAh/g)    (mAh/g)   (mAh/cc)                                ______________________________________                                         9     60        1130       300       162                                     10     83        1130       300       151                                     ______________________________________                                    

Comparative Example 3

Two of the same negative electrodes were obtained in the same manner asin Example 3 except that the composition of the raw materials for PASwas changed to 30 weight parts of the xylene resin and 70 weight partsof the novolak. As to one of the negative electrodes, lithium was notpreviously carried thereon, and the other negative electrode was dopedwith lithium in amounts of 50 mAh/g based on the negative electrode PAS,whereby the lithium was carried thereon. The resultant negativeelectrodes were designated Negative electrode 11 and Negative electrode12, respectively.

Cells were assembled in the same manner as in Example 3, and anevaluation was made using volume capacity. The results are shown in thefollowing Table 7.

                  TABLE 7                                                         ______________________________________                                               Nitrogen                                                                      adsorption                                                                    amount at an                                                                            Total lithium                                                                            Lithium amount                                           adsorption                                                                              amount in the                                                                            originating in the                                                                      Volume                                  Negative                                                                             thickness of                                                                            cell       negative electrode                                                                      capacity                                electrode                                                                            10 Å (cc/g)                                                                         (mAh/g)    (mAh/g)   (mAh/cc)                                ______________________________________                                        11     60        820         0        109                                     12     60        870        50        120                                     ______________________________________                                    

Comparative Example 4

Negative electrodes were obtained in the same manner as in Example 3except that the composition of the raw materials for PAS was changed toa composition of 100 weight parts of the novolak and 10 weight parts ofhexamethylenetetramine, or such a composition that only powdered resol("ResiTop" made by Showa Kobunshi Co., Ltd.) was used as the rawmaterial. These negative electrodes were doped with lithium in an amountof 300 mAh/g based on the negative electrode PAS, whereby the lithiumwas carried thereon. The resultant negative electrodes were designatedNegative electrode 13 and Negative electrode 14, respectively.

Cells were assembled in the same manner as in Example 3, and anevaluation was made using volume capacity. The results are shown in thefollowing Table 8.

                  TABLE 8                                                         ______________________________________                                               Nitrogen                                                                      adsorption                                                                    amount at an                                                                            Total lithium                                                                            Lithium amount                                           adsorption                                                                              amount in the                                                                            originating in the                                                                      Volume                                  Negative                                                                             thickness of                                                                            cell       negative electrode                                                                      capacity                                electrode                                                                            10 Å (cc/g)                                                                         (mAh/g)    (mAh/g)   (mAh/cc)                                ______________________________________                                        13     120       1140       300       130                                     14     132       1120       300       131                                     ______________________________________                                    

(2) Examples of the second preferred embodiment of the invention aredescribed below.

EXAMPLE 5

A formed plate of a phenol resin 0.5 mm thick was put in a siliconcarbide heating element, the inside temperature was increased at a rateof 10° C./hour in an atmosphere of nitrogen, and heat treatment wasconducted up to 650° C. to synthesize an infusible, insoluble substrate(referred to as PAS). Its H/C ratio was 0.22. The resultant PAS platewas ground in an alumina-made pot mill with different grinding times togive PAS powders respectively having the particle size distributionsshown in Table 9 (No. 1, No. 2, No. 3 and No. 4). The particle sizedistribution was measured by dispersing the resultant fine particlesinto water using ultrasonic waves and then using a laserdiffraction-type particle size distribution measuring apparatus.

                                      TABLE 9                                     __________________________________________________________________________    Electrode raw material fine particles                                              Average  Particles having                                                                      Particles having                                                                      Electrode                                       PAS fine                                                                           particle                                                                          50% size                                                                           a particle size                                                                       a particle size                                                                       Negative                                        particle                                                                           size                                                                              (μm)                                                                            of a or less                                                                          of 4a or more                                                                         electrode                                                                          Porosity                                   No.  (μm)                                                                           2a   (%)     (%)     No.  (%)                                        __________________________________________________________________________    1    10.2                                                                              9.5  26      14      15   38                                         2    6.0 4.3  28      28      16   33                                         3    3.6 2.4  31      25      17   29                                         4    2.6 1.6  23      27      18   30                                         __________________________________________________________________________

Then, 100 weight parts of any one of the above PAS powders, and 100weight parts of a solution of 10 weight parts of polyvinylidene fluoridepowder in 90 weight parts of N,N-dimethylformamide were adequately mixedto give a slurry. The slurry was applied onto a copper foil 10 μm thick(a current collector for the negative electrode) using an applicator,dried, and pressed to give a PAS negative electrode 110 μm thick. Theporosity of the negative electrode was determined by impregnating thenegative electrode with propylene carbonate at 25° C. The density of theused propylene carbonate was 1.20 g/cc (measured by a pycnometer). Theresults are shown together in Table 9. 50 weight parts of a solution of10 weight parts of polyvinylidene fluoride powder in 90 weight parts ofN,N-dimethylformamide was adequately mixed with 100 parts ofcommercially available LiCoO₂ (made by Strem Chemicals Co.) and 5 partsof graphite to give a slurry. The slurry was applied onto an aluminumfoil 20 μm thick (a current collector for the positive electrode) usingan applicator, dried, and pressed. Thereby, Positive electrodes 6 and 7were obtained having thicknesses of 160 μm and 180 μm, respectively.

Each of the above negative electrodes was doped with lithium in anamount of 300 mAh/g based on the negative electrode PAS at a constantcurrent (a current was sent whereby 30 mAh/g of lithium could be carriedper hour on the negative electrode PAS), using lithium as a counterelectrode and using a solution of LiPF₆ at a concentration of 1mole/liter in a 1:1 (weight ratio) mixed solvent of propylene carbonateand diethyl carbonate as an electrolytic solution, whereby the lithiumwas carried thereon (lithium originating in the negative electrode).

The above positive electrodes 6 and 7 were combined with the negativeelectrodes 15, 16, 17 and 18 (each 1×1 cm²) so that the total lithiumamount in the cell became about 1,100 mAh/g based on the negativeelectrode PAS, and five kinds of cells as shown in FIG. 1 wereassembled. As the separator, a polypropylene separator 25 μm thick wasused. Further, as the electrolytic solution, a solution of LiPF₆ at aconcentration of 1 mole/liter in a 1:1 (weight ratio) mixed solvent ofpropylene carbonate and diethyl carbonate was used. The total lithiumamount in the cell based on the negative electrode PAS is shown in Table10.

Each of the above cells was charged at a constant current of 0.25 mA/cm²until the cell voltage became 4.3 V, and successively, discharged at aconstant electric current of 0.25 mA/cm² until the cell voltage became2.5 V. This 4.3 V-2.5 V cycle was repeated, and in the third discharge,an evaluation was made using volume capacity (mAh/cc). As the volumestandard, the total of the electrode volumes, the separator volume andthe current collector volumes was used. The results are also shown inTable 10.

                  TABLE 10                                                        ______________________________________                                                         Total lithium                                                                            Lithium amount                                                     amount in the                                                                            originating in the                                                                      Volume                                  Negative                                                                              Positive cell       negative electrode                                                                      capacity                                electrode                                                                             electrode                                                                              (mAh/g)    (mAh/g)   (mAh/cc)                                ______________________________________                                        15      6        1100       300       155                                     16      7        1170       300       173                                     17      7        1105       300       173                                     18      7        1120       300       168                                     ______________________________________                                    

EXAMPLE 6

Positive electrodes 8, 9 and 10 having thicknesses of 240 μm, 210 μm and200 μm, respectively, were obtained in the same manner as in Example 5.The amounts of lithium originating in the negative electrode of Negativeelectrode 17 were made to be 0 mAh/g (comparative), 150 mAh/g and 200mAh/g (the invention), and the resultant negative electrodes werecombined with the above positive electrodes, in the same manner as inExample 5, and cells were assembled and evaluated using volume capacity,in the same manner as in Example 5. The results are shown in Table 11.

                  TABLE 11                                                        ______________________________________                                                         Total lithium                                                                            Lithium amount                                                     amount in the                                                                            originating in the                                                                      Volume                                  Negative                                                                              Positive cell       negative electrode                                                                      capacity                                electrode                                                                             electrode                                                                              (mAh/g)    (mAh/g)   (mAh/cc)                                ______________________________________                                        17      8        1080        0        119                                     17      9        1095       150       148                                     17      10       1100       200       161                                     ______________________________________                                    

When the lithium amount originating in the negative electrode is 0, asufficient capacity was not obtained.

Comparative Example 5

A formed plate of a phenol resin 0.5 mm thick was put in a siliconcarbide heating element, the inside temperature was increased at a rateof 10° C./hour in an atmosphere of nitrogen, and heat treatment wasconducted up to 650° C. to synthesize a PAS. Its H/C ratio was 0.22. Theresultant PAS plate was ground using a jet mill to give PAS powdersrespectively having the particle size distributions shown in Table 4(No. 5, No. 6 and No. 7). Negative electrodes (No. 19, No. 20 and No.21) were obtained and the porosities of them were determined, in thesame manner as in Example 5. The results are shown in Table 12.

                                      TABLE 12                                    __________________________________________________________________________    Electrode raw material fine particles                                              Average  Particles having                                                                      Particles having                                                                      Electrode                                       PAS fine                                                                           particle                                                                          50% size                                                                           a particle size                                                                       a particle size                                                                       Negative                                        particle                                                                           size                                                                              (μm)                                                                            of a or less                                                                          of 4a or more                                                                         electrode                                                                          Porosity                                   No.  (μm)                                                                           2a   (%)     (%)     No.  (%)                                        __________________________________________________________________________    5    22  21   24      22      19   38                                         6    8.5 7.7   4      6       20   46                                         7    2.5 2.1  12      9       21   45                                         __________________________________________________________________________

Positive electrodes 11 and 12 having thicknesses of 150 μm and 130 μm,respectively, were obtained in the same manner as in Example 5.Thereafter, 300 mAh/g of lithium originating in the negative electrodewas carried on each of the negative electrodes of the above No. 19 to 21in the same manner as in Example 5, and an evaluation was conducted inthe same manner as in Example 5. The results are shown in Table 13.

                  TABLE 13                                                        ______________________________________                                                         Total lithium                                                                            Lithium amount                                                     amount in the                                                                            originating in the                                                                      Volume                                  Negative                                                                              Positive cell       negative electrode                                                                      capacity                                electrode                                                                             electrode                                                                              (mAh/g)    (mAh/g)   (mAh/cc)                                ______________________________________                                        19      11       1090       300       116                                     20      12       1120       300       124                                     21      12       1100       300       126                                     ______________________________________                                    

Comparative Example 6

PAS No. 2 of Example 5 was used, and 100 weight parts of the PAS powderwas adequately mixed with 110 weight parts of a solution of 10 weightparts of polyvinylidene fluoride powder in 90 weight parts ofN,N-dimethylformamide to give a slurry. The slurry was applied onto ancopper foil 10 μm thick (a current collector for the negative electrode)using an applicator, and dried to give a PAS negative electrode 110 μmthick. The porosity of the negative electrode was determined byimpregnating it with propylene carbonate at 25° C., and was 46%.

A positive electrode 130 μm thick was obtained in the same manner as inExample 1. Thereafter, 300 mAh/g of lithium originating in the negativeelectrode was carried on the negative electrode in the same manner is inExample 5, and a evaluation was conducted in the same manner as inExample 5. The volume capacity of the resultant cell was 131 mAh/g.

(3) An examples of the third preferred embodiment of the invention isdescribed below.

EXAMPLE 7

A formed plate of a phenol resin 0.5 mm thick was put in a siliconcarbide heating element, the inside temperature was increased at a rateof 10° C./hour in an atmosphere of nitrogen, and heat treatment wasconducted up to 650° C. to synthesize an infusible, insoluble substrate(referred to as PAS). The resultant PAS plate was ground in a pot millto give PAS powder having an average particle size of about 3 μm. ItsH/C ratio was 0.22.

Then, 100 weight parts of the above PAS powder, and 100 weight parts ofa solution of 10 weight parts of polyvinylidene fluoride powder having amelting point of 172° C. in 90 weight parts of N,N-dimethylformamidewere adequately mixed to give a slurry. The slurry was applied onto acopper foil 10 μm thick (a current collector for the negative electrode)using an applicator, dried, and pressed to give a PAS negative electrode210 μm thick wherein both sides of the foil were coated with PAS. ThePAS negative electrode was heat treated in vacuo at 100° C., 160° C.,190° C. or 220° C. to give Negative electrodes 22, 23, 24 and 25.

50 weight parts of a solution of 10 weight parts of polyvinylidenefluoride powder in 90 weight parts of N,N-dimethylformamide wasadequately mixed with 100 parts of commercially available LiCoO₂ (madeby Strem Chemicals Co.) and 5 parts of graphite to give a slurry. Theslurry was applied onto an aluminum foil 20 μm thick (a currentcollector for the positive electrode) using an applicator, dried, andpressed. Thereby was obtained a positive electrode 340 μm thick whereinboth sides of the aluminum foil were coated with LiCoO₂.

Each of the above negative electrodes was doped with lithium in anamount of 300 mAh/g based on the negative electrode PAS at a constantcurrent (a current was sent whereby 30 mAh/g of lithium could be carriedper hour on the negative electrode PAS), using lithium as a counterelectrode and using a solution of LiPF₆ at a concentration of 1mole/liter in a 1:1 (weight ratio) mixed solvent of propylene carbonateand diethyl carbonate as an electrolytic solution, whereby the lithiumwas carried thereon (lithium originating in the negative electrode). Theresultant negative electrodes were designated Negative electrodes 22,23, 24 and 25.

A cylindrical cell as shown in FIG. 2 was assembled using the abovepositive electrode 1, and any one of Negative electrodes 22, 23, 24 and25 (each 4×35 cm²). As the separator, a polypropylene separator 25 μmthick was used. As the positive terminal an aluminum terminal 150 μmthick and 5 mm wide was used, and as the negative terminal, a nickelterminal having the same size as the aluminum terminal was use a, andthese terminals were attached to the ends of both electrodes,respectively. Further, as the electrolytic solution, a solution of LiPF₆at a concentration of 1 mole/liter in a 1:1 (weight ratio) mixed solventof propylene carbonate and diethyl carbonate was used. The total lithiumamount in the cell based on the negative electrode PAS was 1,170 mAh/gon each cell. In this connection, when Negative electrode 1 of 100° C.treatment was used, the electrode peeled off from the metallic foil atthe time of winding of the electrode, and a cell could not be obtained.

Each of the resultant cells was charged at a constant current of 0.25mA/cm² until the cell voltage became 4.3 V, and the internal resistancethereof was measured, and then, successively, the cell was discharged ata constant current of 0.25 mA/cm² until the cell voltage became 2.5 V.This 4.3 V-2.5 V cycle was repeated, and in the third discharge an,evaluation was made using volume capacity (mAh/cc). As the volumestandard, the total of the electrode volumes, the separator volumes andthe current collector volumes was used. The results are also shown inTable 14.

                  TABLE 14                                                        ______________________________________                                                  Heat                                                                Negative  treatment                                                                              Internal resistance                                                                         Volume capacity                              electrode No.                                                                           (°C.)                                                                           (mΩ)    (mAh/cc)                                     ______________________________________                                        22        100      Peeling of the electrode at the                                               time of winding                                            23        160      230           132                                          24        190      120           168                                          25        220      120           164                                          ______________________________________                                    

In the cases of the negative electrodes 24 and 25, which are preferredexamples of the invention, the internal resistances are lower and thevolume capacities are higher, compared with the cases of the negativeelectrodes 22 and 23.

Comparative Example 7

Positive electrode 2 having a thickness of 460 μm was obtained in thesame manner as in Example 7. The sizes of the positive electrode andnegative electrode were made to be equally 4×30 cm².

The amount of lithium originating in any of the negative electrodes wasmade to be 0 mAh/g, and the above positive electrode was combined withany one of the negative electrodes 22, 23, 24 and 25. Then, cells wereassembled and their evaluation was made by their volume capacities, inthe same manner as in Example 7. The total lithium amount in each cellbased on the negative electrode PAS was 1,090 mAh/g. The results areshown in Table 15.

                  TABLE 15                                                        ______________________________________                                                  Heat                                                                Negative  treatment                                                                              Internal resistance                                                                         Volume capacity                              electrode No.                                                                           (°C.)                                                                           (mΩ)    (mAh/cc)                                     ______________________________________                                        22        100      230            99                                          23        160      225           101                                          24        190      160           116                                          25        220      155           118                                          ______________________________________                                    

(4) Examples of the fourth preferred embodiment of the invention aredescribed below.

EXAMPLE 8

A formed plate of a phenol resin 0.5 mm thick was put in a siliconcarbide heating element, the inside temperature was increased at a rateof 10° C./hour in an atmosphere of nitrogen, and heat treatment wasconducted up to 650° C. to synthesize an infusible, insoluble substrate(referred to as PAS). The resultant PAS plate was ground in a disc millto give PAS powder having an average particle size of about 15 μm. ItsH/C ratio was 0.22.

Then, 100 weight parts of the above PAS powder, and 100 weight parts ofa solution of 10 weight parts of polyvinylidene fluoride powder in 90weight parts of N,N-dimethylformamide were adequately mixed to give aslurry. The slurry was applied onto a copper foil 10 μm thick (a currentcollector for the negative electrode) using an applicator, dried, andpressed to give a PAS negative electrode 210 μm thick wherein both sidesof the foil were coated with PAS.

50 weight parts of a solution of 10 weight parts of polyvinylidenefluoride powder in 90 weight parts of N,N-dimethylformamide wasadequately mixed with 100 parts of commercially available LiCoO₂ (madeby Strem Chemicals Co.) and 5 parts of graphite to give a slurry. Theslurry was applied onto an aluminum foil 20 μm thick (a currentcollector for the positive electrode) using an applicator, dried, andpressed. Thereby was obtained a positive electrode 280 μm wherein bothsides of the foil were coated with LiCoO₂.

The above negative electrode was doped with lithium in an amount of 300mAh/g based on the negative electrode PAS at a constant current (acurrent was sent whereby 30 mAh/g of lithium could be carried per houron the negative electrode PAS), using lithium as a counter electrode andusing a solution of LiPF₆ at a concentration of 1 mole/liter in a 1:1(weight ratio) mixed solvent of propylene carbonate and diethylcarbonate as an electrolytic solution, whereby the lithium was carriedthereon (lithium originating in the negative electrode).

A cylindrical cell as shown in FIG. 2 was assembled using the abovepositive electrode and negative electrode (each 4×35 cm²). As theseparator, a polypropylene separator 25 μm thick was used. As thepositive terminal, an aluminum terminal 150 μm thick and 5 mm wide wasused, and as the negative terminal a nickel terminal having the samesize as the aluminum terminal was used, and these terminals wereattached to the ends of both electrodes, respectively. Further, as theelectrolytic solution, a solution of LiPF₆ at a concentration of 1mole/liter in a 1:1 (weight ratio) mixed solvent of propylene carbonateand diethyl carbonate was used. The total lithium amount in the cellbased on the negative electrode PAS was 1,040 mAh/g.

The resultant cell was charged at a constant current of 0.25 mA/cm²until the cell voltage became 4.3 V, and the internal resistance thereofwas measured, and then, successively, the cell was discharged at aconstant current of 0.25 mA/cm² until the cell voltage became 2.5 V.This 4.3 V-2.5 V cycle was repeated, and in the third discharge, anevaluation was made using volume capacity (mAh/cc). As the volumestandard, the total of the electrode volumes, the separator volumes andthe current collector volumes was used. The results are also shown inTable 16.

Comparative Example 8

A positive electrode 380 μm thick was obtained in the same manner as inExample 8. The sizes of the positive electrode and negative electrodewere made to be equally 4×30 cm².

The amount of lithium originating in the negative electrode was made tobe 0 mAh/g, a cell was assembled in the same manner as in Example 8, andits evaluation was made by volume capacity. The total lithium amount inthe cell based on the negative electrode PAS was 1,010 mAh/g. Theresults are shown in Table 16.

Comparative Example 9

In Example 8, metallic lithium in an amount of 300 mAh/g (about 12 μm)was stuck on the negative electrode PAS, and then, two cylindrical cellsas in Example 8 were assembled. The cells were left alone at roomtemperature for 3 days, and when one of them was decomposed, themetallic lithium completely disappeared. An evaluation was made byvolume capacity in the same manner as in Example 8. The total lithiumamount in this cell was 1,040 mAh/g. The results are shown in Table 16.

When the lithium amount originating in the negative electrode was 0, asufficient capacity could not be obtained, and when lithium originatingin the negative electrode was carried in the cell, the internalresistance of the cell was increased and the cell capacity was lowered.

EXAMPLE 9

In Example 8, metallic lithium (about 200 μm) was stuck on the negativeelectrode PAS, the resultant matter was held between polypropyleneplates, each being 2 mm thick, and lithium originating in the negativeelectrode was carried on the negative electrode PAS in the sameelectrolytic solution as in Example 1. About 40 minutes later, themetallic lithium was peeled from the PAS negative electrode and the PASnegative electrode was doped with 300 mAh/g of lithium. Thereafter, acylindrical cell as in Example 8 was assembled and an evaluation wasmade by volume capacity in the same manner as in Example 8. The totallithium amount in this cell was 1,040 mAh/g. The results are shown inTable 16.

EXAMPLE 10

In Example 8, lithium originating in the negative electrode was carriedon the negative electrode PAS by short-circuiting the counter electrodemetallic lithium (about 200 μm) and the negative electrode PAS. Thereby,the negative electrode PAS could be doped with 300 mAh/g of lithium inabout 35 minutes. Thereafter, a cylindrical cell as in Example 8 wasassembled, and an evaluation was made by volume capacity in the samemanner as in Example 8. The total lithium amount in this cell was 1,040mAh/g. The results are shown in Table 16.

                                      TABLE 16                                    __________________________________________________________________________               Lithium originating                                                                    Lithium amount originating                                                                Volume                                                                             Internal                                            in the negative                                                                        in the negative electrode                                                                 capacity                                                                           resistance                               Negative electrode No.                                                                   electrode                                                                              (mAh/g)     (mAh/cc)                                                                           (mΩ)                               __________________________________________________________________________    Example 8  Before assembly                                                                        300         151  160                                      Comparative example 8                                                                    Before assembly                                                                         0           98  200                                      Comparative example 9                                                                    After assembly                                                                         300         117  360                                      Example 9  Before assembly                                                                        300         149  150                                      Example 10 Before assembly                                                                        300         153  150                                      __________________________________________________________________________

(5) An example of the fifth preferred embodiment of the invention isdescribed below.

EXAMPLE 11

A formed plate of a phenol resin 0.5 mm thick was put in a siliconcarbide heating element, the inside temperature was increased at a rateof 10° C./hour in an atmosphere of nitrogen, and heat treatment wasconducted up to 650° C. to synthesize an infusible, insoluble substrate(referred to as PAS). The resultant PAS plate was ground in a disc millto give PAS powder having an average particle size of about 15 μm. ItsH/C ratio was 0.22.

Then, 100 weight parts of the above PAS powder, and 100 weight parts ofa solution of 10 weight parts of polyvinylidene fluoride powder in 90weight parts of N,N-dimethylformamide were adequately mixed to give aslurry. The slurry was applied onto a copper foil 10 μm thick (a currentcollector for the negative electrode) using an applicator, dried, andpressed to give a PAS negative electrode 210 μm thick wherein both sidesof the foil were coated with PAS.

50 weight parts of a solution of 10 weight parts of polyvinylidenefluoride powder in 90 weight parts of N,N-dimethylformamide wasadequately mixed with 100 parts of commercially available LiCoO₂ (madeby Strem Chemicals Co.) and 5 parts of graphite to give a slurry. Theslurry was applied onto a aluminum foil 20 μm thick (a current collectorfor the positive electrode) using an applicator, dried, and pressed.Thereby was obtained a positive electrode 280 μm thick wherein bothsides of the foil were coated with LiCoO₂.

An electrolytic cell having a lithium reference electrode was assembled,using the above negative electrode, and lithium as a counter electrode,and using, as the electrolytic solution, a solution of LiPF₆ at aconcentration of 1 mole/liter in a 1:1 (weight ratio) mixed solvent ofpropylene carbonate and diethyl carbonate. A constant voltage wasapplied so that the PAS negative electrode became +20 mV, 0 mV, -20 mV,-50 mV or -100 mV, based on the lithium reference electrode, and timeneeded for carrying 300 mAh/g of lithium originating in the negativeelectrode was measured. The results are shown in Table 17.

A cell as shown in FIG. 1 was assembled using the above positiveelectrode 1 and negative electrode (each 1×1 cm²) . As the separator, apolypropylene separator 25 μm thick was used. The total lithium amountin the cell based on the negative electrode PAS was 1,040 mAh/g.

Each of the resultant cells was charged at a constant current of 0.25mA/cm² until the cell voltage became 4.3 V, and then, successively, thecell was discharged at a constant current of 0.25 mA/cm² until the cellvoltage became 2.5 V. This 4.3 V-2.5 V cycle was repeated, and in thethird discharge, an evaluation was made using volume capacity (mAh/cc).As the volume standard, the total of the electrode volumes, theseparator volumes and the current collector volumes was used. Theresults are also shown in Table 17.

                  TABLE 17                                                        ______________________________________                                                     Time needed for carrying                                         Voltage applied                                                                            lithium originating in the                                                                    Volume                                           on the negative                                                                            negative electrode                                                                            capacity                                         electrode lithium                                                                          (minute)        (mAh/cc)                                         ______________________________________                                        +20 mV       43 minutes      152                                              Comparison   (No deposition of lithium)                                          0 mV      29 minutes      153                                              The invention                                                                              (No deposition of lithium)                                       -20 mV       24 minutes      149                                              The invention                                                                              (No deposition of lithium)                                       -50 mV       20 minutes      152                                              The invention                                                                              (No deposition of lithium)                                       -100 mV      16 minutes      150                                              The invention                                                                              (No deposition of lithium)                                       ______________________________________                                    

Comparative Example 10

In Example 11, metallic lithium (about 200 μm) was adhered to thenegative electrode PAS, the resultant matter was held betweenpolypropylene plates, each being 2 mm thick, and lithium originating inthe negative electrode was carried on the negative electrode PAS in thesame electrolytic solution as in Example 1. About 40 minutes later, themetallic lithium was peeled from the PAS negative electrode and the PASnegative electrode was doped with 300 mAh/g of lithium. It takes moretime, compared with the case where a negative voltage was applied.

Comparative Example 11

In Example 11, lithium originating in the negative electrode was carriedon the negative electrode PAS by short-circuiting the counter electrodemetallic lithium (about 200 μm) and the negative electrode PAS. Thereby,the negative electrode PAS could be doped with 300 mAh/g of lithium inabout 35 minutes. It takes more time, compared with the case where anegative voltage was applied.

Comparative Example 12

A formed plate of a phenol resin 0.5 mm thick was put in a siliconcarbide heating element, the inside temperature was increased at a rateof 10° C./hour in an atmosphere of nitrogen, and heat treatment wasconducted up to 1,000° C. to give a carbonaceous material. The resultantPAS plate was ground in a disc mill to give a powder of the carbonaceousmaterial having an average particle size of about 13 μm. Its H/C ratiowas 0.02.

The carbonaceous material was made into an electrode in the same manneras in Example 11, and lithium originating in the negative electrode wascarried thereon in the same manner as in Example 11. In the case of +20mV, the time needed for the carrying was 50 minutes, and in the case of0 mV, the time needed for the carrying was 45 minutes, and when -20 mV,-50 mV and -100 mV were applied, respectively, metallic lithium wasdeposited on the negative electrode carbonaceous material. When theresultant negative electrodes were left alone, the metallic lithiumdisappeared after about 30 hours after the start of the leaving alone,but these methods are not practical as methods for carrying lithiumoriginating in the negative electrode.

Further, when a cell similar to that in Example 11 was assembled usingthe negative electrode prepared by the application of +20 mV, andevaluated, a large amount of metallic lithium was deposited on thenegative electrode after the cycle was conducted three times.

(6) Examples of the sixth preferred embodiment of the invention aredescribed below.

EXAMPLE 12

A formed plate of a phenol resin 0.5 mm thick was put in a siliconcarbide heating element, the inside temperature was increased at a rateof 10° C./hour in an atmosphere of nitrogen, and heat treatment wasconducted up to 650° C. to synthesize an infusible, insoluble substrate(referred to as PAS). The resultant PAS plate was ground in a disc millto give PAS powder having an average particle size of about 15 μm. ItsH/C ratio was 0.22.

Then, 100 weight parts of the above PAS powder, and 100 weight parts ofa solution of 10 weight parts of polyvinylidene fluoride powder in 90weight parts of N,N-dimethylformamide were adequately mixed to give aslurry. The slurry was applied onto a copper foil 10 μm thick (a currentcollector for the negative electrode) using an applicator, dried, andpressed to give a PAS negative electrode 210 μm thick wherein both sidesof the foil were coated with PAS.

50 weight parts of a solution of 10 weight parts of polyvinylidenefluoride powder in 90 weight parts of N,N-dimethylformamide wasadequately mixed with 100 parts of commercially available LiCoO₂ (madeby Strem Chemicals Co.) and 5 parts of graphite to give a slurry. Theslurry was applied onto a aluminum foil 20 μm thick (a current collectorfor the positive electrode) using an applicator, dried, and pressed.Thereby was obtained a positive electrode 280 μm thick wherein bothsides of the foil were coated with LiCoO₂.

The above negative electrode was doped with lithium in an amount of 300mAh/g based on the negative electrode PAS at a constant current (acurrent was sent whereby 30 mAh/g of lithium could be carried per houron the negative electrode PAS), using lithium as a counter electrode andusing a solution of LiPF₆ at a concentration of 1 mole/liter inpropylene carbonate and diethyl carbonate as an electrolytic solution,whereby the lithium was carried thereon (lithium originating in thenegative electrode).

A cell as shown in FIG. 1 was assembled using the above positiveelectrode and negative electrode (each 1×1 cm²). As the separator, apolypropylene separator 25 μm thick was used. Further, as theelectrolytic solution, a solution of LiPF₆ at a concentration of 1mole/liter in a 1:1 (weight ratio) mixed solvent of propylene carbonateand diethyl carbonate was used. The total lithium amount in the cellbased on the negative electrode PAS was 1,040 mAh/g.

The resultant cell was charged at a constant current of 0.25 mA/cm²until the cell voltage became 4.3 V, and then, successively, the cellwas discharged at a constant electric current of 0.25 mA/cm² until thecell voltage became 2.5 V. This 4.3 V-2.5 V cycle was repeated, and whenin the third discharge, an evaluation was made using volume capacity(mAh/cc), it was 169 mAh/cc. As the volume standard, the total of theelectrode volumes, the separator volume and the current collectorvolumes was used.

Comparative Example 13

A cell was assembled in the same manner as in Example 1 except that asto lithium originating in the negative electrode, a solution of LiPF₆ ata concentration of 1 mole/liter in a 1:1 (weight ratio) mixed solvent ofpropylene carbonate and diethyl carbonate was used, and an evaluationwas made using volume capacity, which was found to be 155 mAh/cc.

EXAMPLE 13

A cell was assembled in the same manner as in Example 12 except that asto lithium originating in the negative electrode, a solution of LiPF₆ ata concentration of 1 mole/liter in a 1:1 (weight ratio) mixed solvent ofpropylene carbonate and diethyl carbonate was used, and an evaluationwas made using volume capacity, which was found to be 167 mAh/cc.

The volume capacity in this example is about 10% higher than that inComparative example 13.

We claim:
 1. An organic electrolytic cell comprising a positiveelectrode, a negative electrode and a solution of lithium salt in anaprotic organic solvent as an electrolytic solution, wherein(1) thepositive electrode contains a metallic oxide, (2) the negative electrodecomprises an infusible, insoluble substrate having a polyacene skeletalstructure and a hydrogen/carbon atomic ratio of 0.5 to 0.05, saidsubstrate being a heat-treated product of an aromatic condensationpolymer, and (3) the total amount of lithium contained in the cellcorresponds to a charge and discharge capacity of at least 500 mAh/g,and the amount of lithium originating in the negative electrodecorresponds to a charge and discharge capacity of at least 100 mAh/g,based on the infusible, insoluble substrate.
 2. The organic electrolyticcell according to claim 1, wherein the negative electrode additionallycomprises a binder of a fluorine-containing polymer having afluorine/carbon atomic ratio of under 1.5 but is at least 0.75.
 3. Theorganic electrolytic cell according to claim 2, wherein thefluorine-containing polymer is polyvinylidene fluoride.
 4. The organicelectrolytic cell according to claim 1, wherein a lithium-containingmetallic oxide is used as the positive electrode.
 5. An organicelectrolytic cell comprising a positive electrode, a negative electrodeand a solution of a lithium salt in an aprotic organic solvent as anelectrolytic solution, wherein(1) the positive electrode contains ametallic oxide, (2) the negative electrode comprises an infusible,insoluble substrate having a polyacene skeletal structure and ahydrogen/carbon atomic ratio of 0.5 to 0.05, said substrate being aheat-treated product of an aromatic condensation polymer, and (3) thetotal amount of lithium contained in the cell corresponds to a chargeand discharge capacity of at least 500 mAh/g, and the amount of lithiumoriginating in the negative electrode corresponds to a charge anddischarge capacity of at least 100 mAh/g, based on the infusible,insoluble substrate, the infusible, insoluble substrate being such thatthe amount of adsorbed gas at a nitrogen adsorption thickness of 10obtained from a nitrogen adsorption isotherm is no more than 100 cc/g.6. The organic electrolytic cell according to claim 5, wherein thenegative electrode additionally comprises a binder, the binder being afluorine-containing polymer having a fluorine/carbon atomic ratio ofunder 1.5 but is at least 0.75.
 7. The organic electrolytic cellaccording to claim 6, wherein the fluorine-containing polymer is apolyvinylidene fluoride.
 8. The organic electrolytic cell according toclaim 5, wherein the positive electrode is a lithium-containing metallicoxide.
 9. An organic electrolytic cell comprising a positive electrode,a negative electrode and a solution of a lithium salt in an aproticorganic solvent as an electrolytic solution, wherein(1) the positiveelectrode contains a metallic oxide, (2) the negative electrodecomprises an infusible, insoluble substrate having a polyacene skeletalstructure and a hydrogen/carbon atomic ratio of 0.5 to 0.05, saidsubstrate being a heat-treated product of an aromatic condensationpolymer, and (3) the total amount of lithium contained in the cellcorresponds to a charge and discharge capacity of at least 500 mAh/g,and the amount of lithium originating in the negative electrodecorresponds to a charge and discharge capacity of at least 100 mAh/g,based on the infusible, insoluble substrate, the infusible, insolublesubstrate being composed of particles having an average particle size ofno more than 20 μm.
 10. An organic electrolytic cell comprising apositive electrode, a negative electrode and a solution of a lithiumsalt in an aprotic organic solvent as an electrolytic solution,wherein(1) the positive electrode contains a metallic oxide, (2) thenegative electrode comprises an infusible, insoluble substrate having apolyacene skeletal structure and a hydrogen/carbon atomic ratio of 0.5to 0.05, said substrate being a heat-treated product of an aromaticcondensation polymer, and (3) the total amount of lithium contained inthe cell corresponds to a charge and discharge capacity of at least 500mAh/g, and the amount of lithium originating in the negative electrodecorresponds to a charge and discharge capacity of at least 100 mAh/g,based on the infusible, insoluble substrate, the negative electrodebeing obtained by forming the infusible, insoluble substrate on ametallic foil using a thermoplastic binder to make a resultant form, andthen heating the resultant form at a temperature at least equal to themelting point of the thermoplastic binder.
 11. An organic electrolyticcell comprising a positive electrode, a negative electrode and asolution of a lithium salt in an aprotic organic solvent as anelectrolytic solution, wherein(1) the positive electrode contains ametallic oxide, (2) the negative electrode comprises an infusible,insoluble substrate having a polyacene skeletal structure and ahydrogen/carbon atomic ratio of 0.5 to 0.05, said substrate being aheat-treated product of an aromatic condensation polymer, and (3) thetotal amount of lithium contained in the cell corresponds to a chargeand discharge capacity of at least 500 mAh/g, and the amount of lithiumoriginating in the negative electrode corresponds to a charge anddischarge capacity of at least 100 mAh/g based on the infusible,insoluble substrate, the lithium in the negative electrode beingpreviously carried on the infusible, insoluble substrate prior toassembly of the cell.
 12. An organic electrolytic cell comprising apositive electrode, a negative electrode and a solution of a lithiumsalt in an aprotic organic solvent as an electrolytic solution,wherein(1) the positive electrode contains a metallic oxide, (2) thenegative electrode comprises an infusible, insoluble substrate having apolyacene skeletal structure and a hydrogen/carbon atomic ratio of 0.5to 0.05, said substrate being a heat-treated product of an aromaticcondensation polymer, and (3) the total amount of lithium contained inthe cell corresponds to a charge and discharge capacity of at least 500mAh/g, and the amount of lithium originating in the negative electrodecorresponds to a charge and discharge capacity of at least 100 mAh/g,based on the infusible, insoluble substrate, the lithium originating inthe negative electrode being electrochemically carried through theapplication of an electric potential no greater than the electricpotential of metallic Li.
 13. An organic electrolytic cell comprising apositive electrode, a negative electrode and a solution of a lithiumsalt in an aprotic organic solvent as an electrolytic solution,wherein(1) the positive electrode contains a metallic oxide, (2) thenegative electrode comprises an infusible, insoluble substrate having apolyacene skeletal structure and a hydrogen/carbon atomic ratio of 0.5to 0.05, said substrate being a heat-treated product of an aromaticcondensation polymer, and (3) the total amount of lithium contained inthe cell corresponds to a charge and discharge capacity of at least 500mAh/g, and the amount of lithium originating in the negative electrodecorresponds to a charge and discharge capacity of at least 100 mAh/g,based on the infusible, insoluble substrate, the lithium originating inthe negative electrode being electrochemically carried through the useof a solution of a lithium salt in a cyclic carbonate solvent.